'EditItem' is not allowed for this view. WPF .NET 4 / EF 4.1 - Master - Detail

Ok, in order to try to find an answer for this question I have made an even simpler project, using the AdventureWorks database.

I created a Model from the Vendor and PurchaseOrderHeader tables - added them as a datasource to the project, and have the following code:

XAML:

<Window x:Class="EFDbContextTest.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="MainWindow" Height="569" Width="1130" mc:Ignorable="d" xmlns:d="http://schemas.microsoft.com/expression/blend/2008" xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" xmlns:my="clr-namespace:EFDbContextTest;assembly=EFDbContextTest" Loaded="Window_Loaded">
<Window.Resources>
    <CollectionViewSource x:Key="vendorViewSource" d:DesignSource="{d:DesignInstance my:Vendor, CreateList=True}" />
    <CollectionViewSource x:Key="vendorPurchaseOrderHeadersViewSource" Source="{Binding Path=PurchaseOrderHeaders, Source={StaticResource vendorViewSource}}" />
</Window.Resources>
<Grid DataContext="{StaticResource vendorViewSource}">
    <DataGrid AutoGenerateColumns="False" EnableRowVirtualization="True" Height="200" HorizontalAlignment="Left" ItemsSource="{Binding}" Margin="12,12,0,0" 
              Name="vendorDataGrid" RowDetailsVisibilityMode="VisibleWhenSelected" VerticalAlignment="Top" Width="1084" IsSynchronizedWithCurrentItem="True" 
              SelectedValuePath="VendorID">
        <DataGrid.Columns>
            <DataGridTextColumn x:Name="accountNumberColumn" Binding="{Binding Path=AccountNumber}" Header="Account Number" Width="SizeToHeader" />
            <DataGridCheckBoxColumn x:Name="activeFlagColumn" Binding="{Binding Path=ActiveFlag}" Header="Active Flag" Width="SizeToHeader" />
            <DataGridTextColumn x:Name="creditRatingColumn" Binding="{Binding Path=CreditRating}" Header="Credit Rating" Width="SizeToHeader" />
            <DataGridTemplateColumn x:Name="modifiedDateColumn" Header="Modified Date" Width="SizeToHeader">
                <DataGridTemplateColumn.CellTemplate>
                    <DataTemplate>
                        <DatePicker SelectedDate="{Binding Path=ModifiedDate, Mode=TwoWay, ValidatesOnExceptions=true, NotifyOnValidationError=true}" />
                    </DataTemplate>
                </DataGridTemplateColumn.CellTemplate>
            </DataGridTemplateColumn>
            <DataGridTextColumn x:Name="nameColumn" Binding="{Binding Path=Name}" Header="Name" Width="SizeToHeader" />
            <DataGridCheckBoxColumn x:Name="preferredVendorStatusColumn" Binding="{Binding Path=PreferredVendorStatus}" Header="Preferred Vendor Status" Width="SizeToHeader" />
            <DataGridTextColumn x:Name="purchasingWebServiceURLColumn" Binding="{Binding Path=PurchasingWebServiceURL}" Header="Purchasing Web Service URL" Width="SizeToHeader" />
            <DataGridTextColumn x:Name="vendorIDColumn" Binding="{Binding Path=VendorID}" Header="Vendor ID" Width="SizeToHeader" />
        </DataGrid.Columns>
    </DataGrid>
    <DataGrid AutoGenerateColumns="False" EnableRowVirtualization="True" Height="200" HorizontalAlignment="Left" 
              ItemsSource="{Binding Source={StaticResource vendorPurchaseOrderHeadersViewSource}}" Margin="12,218,0,0" Name="purchaseOrderHeadersDataGrid" 
              RowDetailsVisibilityMode="VisibleWhenSelected" VerticalAlignment="Top" Width="1084" IsSynchronizedWithCurrentItem="True">
        <DataGrid.Columns>
            <DataGridTextColumn x:Name="employeeIDColumn" Binding="{Binding Path=EmployeeID}" Header="Employee ID" Width="SizeToHeader" />
            <DataGridTextColumn x:Name="freightColumn" Binding="{Binding Path=Freight}" Header="Freight" Width="SizeToHeader" />
            <DataGridTemplateColumn x:Name="modifiedDateColumn1" Header="Modified Date" Width="SizeToHeader">
                <DataGridTemplateColumn.CellTemplate>
                    <DataTemplate>
                        <DatePicker SelectedDate="{Binding Path=ModifiedDate, Mode=TwoWay, ValidatesOnExceptions=true, NotifyOnValidationError=true}" />
                    </DataTemplate>
                </DataGridTemplateColumn.CellTemplate>
            </DataGridTemplateColumn>
            <DataGridTemplateColumn x:Name="orderDateColumn" Header="Order Date" Width="SizeToHeader">
                <DataGridTemplateColumn.CellTemplate>
                    <DataTemplate>
                        <DatePicker SelectedDate="{Binding Path=OrderDate, Mode=TwoWay, ValidatesOnExceptions=true, NotifyOnValidationError=true}" />
                    </DataTemplate>
                </DataGridTemplateColumn.CellTemplate>
            </DataGridTemplateColumn>
            <DataGridTextColumn x:Name="purchaseOrderIDColumn" Binding="{Binding Path=PurchaseOrderID}" Header="Purchase Order ID" Width="SizeToHeader" />
            <DataGridTextColumn x:Name="revisionNumberColumn" Binding="{Binding Path=RevisionNumber}" Header="Revision Number" Width="SizeToHeader" />
            <DataGridTemplateColumn x:Name="shipDateColumn" Header="Ship Date" Width="SizeToHeader">
                <DataGridTemplateColumn.CellTemplate>
                    <DataTemplate>
                        <DatePicker SelectedDate="{Binding Path=ShipDate, Mode=TwoWay, ValidatesOnExceptions=true, NotifyOnValidationError=true}" />
                    </DataTemplate>
                </DataGridTemplateColumn.CellTemplate>
            </DataGridTemplateColumn>
            <DataGridTextColumn x:Name="shipMethodIDColumn" Binding="{Binding Path=ShipMethodID}" Header="Ship Method ID" Width="SizeToHeader" />
            <DataGridTextColumn x:Name="statusColumn" Binding="{Binding Path=Status}" Header="Status" Width="SizeToHeader" />
            <DataGridTextColumn x:Name="subTotalColumn" Binding="{Binding Path=SubTotal}" Header="Sub Total" Width="SizeToHeader" />
            <DataGridTextColumn x:Name="taxAmtColumn" Binding="{Binding Path=TaxAmt}" Header="Tax Amt" Width="SizeToHeader" />
            <DataGridTextColumn x:Name="totalDueColumn" Binding="{Binding Path=TotalDue}" Header="Total Due" Width="SizeToHeader" />
            <DataGridTextColumn x:Name="vendorIDColumn1" Binding="{Binding Path=VendorID}" Header="Vendor ID" Width="SizeToHeader" />
        </DataGrid.Columns>
    </DataGrid>
</Grid>

C#:

using System;
using System.Collections.Generic;
using System.Data.Entity;
using System.Linq;
using System.Text;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
开发者_如何学编程using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;


namespace EFDbContextTest
{
    /// <summary>
    /// Interaction logic for MainWindow.xaml
    /// </summary>
    public partial class MainWindow : Window
    {
        Entities _context = new Entities();

        public MainWindow()
        {
            InitializeComponent();
        }

        private void Window_Loaded(object sender, RoutedEventArgs e)
        {
            System.Windows.Data.CollectionViewSource vendorViewSource =
                ((System.Windows.Data.CollectionViewSource)(this.FindResource("vendorViewSource")));
        _context.Vendors.Include("PurchaseOrderHeaders").Load();
        vendorViewSource.Source = _context.Vendors.Local;

        }
    }
}

So, both grids are on the Window, you can edit/delete/update the Master grid like there's no tomorrow - as soon as you try to click into any cell on the detail grid you get the error 'EditItem' is not allowed for this view.

I have to be missing something here, because this happens to me in several instances where I have a Master-Detail view using EF 4.1 - help!

If the PurchaseOrderHeaders collection property in your Vendor class is of type ICollection<T> then this could be source of your problem. To get a datagrid which allows editing the source collection must be of type IList<T> or any type which implements IList<T> like List<T> or ObservableCollection<T>. You will probably need to change the collection type of PurchaseOrderHeaders in your model class accordingly.

More detailed explanation is here: Getting Readonly Databind using EF POCO Objects

Edit

According to @Allon Guralnek's comment below it is necessary to implement the non-generic IList interface to get an editable DataGrid. This is the case for ObservableCollection<T> and List<T>. Other implementations which only implement the generic IList<T> but not the non-generic IList won't make the DataGrid editable.